The invention relates to a main braking device for a line-powered hand tool, in accordance with claim 1.
Main-braked commutator motors are known in various layouts and technologies.
In DE-PS 15 88 380 an arrangement is described for reverse current braking of a DC series-wound motor, fed from a battery via a pulse control device, with two reversing contactors reversing the polarity of its field winding. By means of two diodes (D1, D2), each of which is permanently connected directly to the field winding by one contact (E, F), and by means of an actuator which operates the reversing contactors (1,2) sequentially in the correct order, the intent is to prevent switching sparks from being generated when the motor is shifted to reverse current braking. Reverse current braking serves primarily to brake the motor to a stop so that it can be run up to speed again in the opposite direction of rotation.
Reverse current braking of this type, as described in DE-PS 15 88 380, is not suitable for a line-powered power tool (angle grinder, manual circular saw) with a high power consumption, as the requisite devices for safe reverse current braking are not available.
DE-AS 12 25 223 describes a regenerative braking circuit for AC series-wound motors which are serially excited during braking, whose field excitation is polarity-reversed during braking by using means to limit braking current and to prevent self-excitation with non-main frequency. It employs a circuit configuration controlled by braking current, which interrupts the current direction of the decayed half-wave with each zero crossing of the regenerative braking current.
However, there is no application for a regenerative braking circuit of this type for power tools equipped with dangerous attachments. DE 23 48 880 B 2 describes an automatic washing machine drive with an electrically brakeable series-wound commutator motor, whose armature winding is by-passed during braking. The speed (rpm) of the series-wound motor can be controlled through a semi-conductor circuit configuration (1), and a switch is provided by which, when it is in its closed position, the armature winding (2) is by-passed and the field winding is also connected via the semi-conductor circuit configuration directly to the power main, and the field current can be changed by means of the semi-conductor circuit configuration.
Even the circuit configuration described in DE 23 48 880 is not suitable for a line-powered power tool, as the positive series-wound braking desirable in the case of power tools cannot be implemented by this method. The basic object of the invention is to create a main braking device for line-powered power tools, whereby high-power standard commutator motors can be braked safely by means of gentle high-speed braking in order to be able to use a main braking device of this type in a power tool fitted with a dangerous attachments, such as a manual circular saw, angle grinder, or similar.
This objective is achieved through the properties described under claim 1.
Additional configurations of the invention can be found in the sub-claims and the ensuing description.
In the case of an arrangement of the type described at the beginning, the invention can be seen in that adequate devices are assigned to the electronics of the line-powered power tool to enable the main for brake operation, and they are capable of positive identification to initiate brake operation, and also in that a speed detecting device is assigned to the commutator motor of the line-powered power tool which is used during motor operation and also during brake operation to identify the braking procedure and that the motor is not running, and in that the power on/off-switch for the line-powered power tool contains two two-way switches and a main disconnect, which are operated simultaneously through an actuator, where the main disconnect has an automatic mechanical disconnect delay for the braking period, or the main is disconnected by a relay after the braking process.